PDF(Pubmed)
Abstract：
Pretreatment of lignocellulose yields a complex sugar mixture that potentially can be converted into bioethanol and other chemicals by engineered yeast. One approach to overcome competition between sugars for uptake and metabolism is the use of a consortium of specialist strains capable of efficient conversion of single sugars. Here, we show that maltose inhibits cell growth of a xylose-fermenting specialist strain IMX730.1 that is unable to utilize glucose because of the deletion of all hexokinase genes. The growth inhibition cannot be attributed to a competition between maltose and xylose for uptake. The inhibition is enhanced in a strain lacking maltase enzymes (dMalX2) and completely eliminated when all maltose transporters are deleted. High-level accumulation of maltose in the dMalX2 strain is accompanied by a hypotonic-like transcriptional response, while cells are rescued from maltose-induced cell death by the inclusion of an extracellular osmolyte such as sorbitol. These data suggest that maltose-induced cell death is due to high levels of maltose uptake causing hypotonic-like stress conditions and can be prevented through engineering of the maltose transporters. Transporter engineering should be included in the development of stable microbial consortia for the efficient conversion of lignocellulosic feedstocks.
摘要：
木质纤维素的预处理产生复杂的糖混合物,其潜在地可以通过工程酵母转化为生物乙醇和其他化学品。克服糖之间用于摄取和代谢的竞争的一种方法是使用能够有效转化单糖的专业菌株联盟。在这里，我们显示麦芽糖抑制木糖发酵专业菌株IMX730.1的细胞生长，该菌株由于所有己糖激酶基因的缺失而无法利用葡萄糖。生长抑制不能归因于麦芽糖和木糖之间对摄取的竞争。在缺乏麦芽糖酶（dMalX2）的菌株中，抑制作用得到增强，当所有麦芽糖转运蛋白缺失时，抑制作用将完全消除。dMalX2菌株中麦芽糖的高水平积累伴随着低张样转录反应，而细胞从麦芽糖诱导的细胞死亡中获救，通过包含细胞外渗透物，如山梨糖醇。这些数据表明，麦芽糖诱导的细胞死亡是由于高水平的麦芽糖摄取导致低渗样应激条件，并且可以通过麦芽糖转运蛋白的工程化来预防。转运蛋白工程应包括在稳定的微生物聚生体的开发中，以有效转化木质纤维素原料。
